1. Field of the Invention
The current invention concerns a novel, safe, nonirritating and physiologically compatible inhalable aztreonam formulation suitable for treatment of pulmonary bacterial infections caused by gram negative bacteria, such as Escherichia coli, Enterobacteria species, Klebsiella pneumoniae, K. oxytoca, Proteus mirabilis, Pseudomonas aeruginosa, Serratia marcescens, Haemophilus influenzae, Burkholderia cepacia, Stenotrophomonas maltophilia, Alcaligenes xylosoxidans. In particular, the invention concerns the inhalable formulation comprising aztreonam or a pharmaceutically acceptable salt thereof suitable for treatment and prophylaxis of acute and chronic pulmonary bacterial infections, particularly those caused by gram-negative bacteria Burkholderia cepacia, Stenotrophomonas maltophilia, Alcaligenes xylosoxidans, and multidrug resistant Pseudomonas aeruginosa which are resistant to treatment with other antibiotics. The inhalable formulation is delivered as an aerosol or as an inhalable dry powder. For aerosolization, about 1 to about 250 mg of aztreonam is dissolved in about 1 to about 5 ml of saline or other aqueous solution having a pH between 4.5 and 7.5, delivered to the lung endobronchial space in an aerosol having mass medium average diameter particles predominantly between 1 to 5μ using a nebulizer able to atomize the aztreonam solution into particles of required sizes. The aerosol formulation has a small volume yet delivers a therapeutically efficacious dose of aztreonam to the site of the infection in amounts sufficient to treat bacterial pulmonary infections. A combination of the novel formulation with the atomizing nebulizer permits about 50% delivery of the administered dose of aztreonam into airways. For delivery of dry inhalable powder, aztreonam is milled or spray dried to particle sizes between about 1 and 5μ. The dry powder formulation or a reconstituted aztreonam solid for aerosolization have a long shelf-life and storage stability.
2. Background and Related Disclosures
A wide variety of gram-negative bacteria cause severe pulmonary infections. Many of these bacteria are or become resistant to commonly used or specialty antibiotics and require treatment with new types of antibiotics. The pulmonary infections caused by gram-negative bacteria are particularly dangerous to patients who have decreased immunoprotective responses, such as for example cystic fibrosis and HIV patients, patients with bronchiectasis or those on mechanical ventilation.
Therefore, the bacterial respiratory infections caused by organisms resistant to antibiotics continues to be a major problem, particularly in immunocompromised or hospitalized patients, as well as in patients assisted by mechanical ventilation, as described in Principles and Practice of Infectious Diseases, Eds. Mandel, G. L., Bennett, J. E., and Dolin, R., Churchill Livingstone Inc., New York, N.Y., (1995).
Currently accepted therapy for severe bacterial respiratory tract infections, particularly for treatment of pneumonia in patients with underlying illnesses, includes treatment with various intravenous antibacterial agents, often used in two or three way combination. Most of these agents are not suitable, available or FDA approved for either oral or aerosol dosing. In some cases the efficacious systemic intravenous or oral dose, if oral delivery is possible, requires doses which are borderline or outright toxic thus often preventing a use of perfectly good antibiotic for treatment of the pulmonary infections.
Thus it would be desirable to have available other modes of delivery routes of these antibiotics enabling a targeted delivery of smaller amounts of the antibiotic to endobronchial space of airways for treatment of these bacterial infections rather than administering the antibiotic systemically in large amounts.
Additionally, chronically ill patients are often affected with infections caused by bacteria which are largely resistant to commonly used antibiotics or, upon extended use of certain antibiotic, often develop strong resistance to such antibiotic. For example, chronic pulmonary colonization with Pseudomonas aeruginosa in patients with cystic fibrosis is a principal cause of their high mortality. When established, the chronic pulmonary infection is very difficult, if not impossible, to eradicate. More than 60% of cystic fibrosis patients are colonized with Pseudomonas aeruginosa bacterium strains which are largely resistant to regular and specialty antibiotics, such as piperacillin, ticarcillin, meropenem, netilmicin and only little sensitive to azlocillin, ciprofloxacin, timentin and ceftazidime. Many strains have also been shown to develop resistance to tobramycin and to colistin, if used continuously.
Often, after prolonged antibiotic therapy, a superinfection with organisms intrinsically resistant to oral, intravenous or inhaled antibiotics develops in patients with cystic fibrosis and other chronic pulmonary infections. The four most common drug resistant organisms are Burkholderia cepacia, Stenotrophomonas maltophilia, Alcaligenes xylosoxidans, and multidrug resistant Pseudomonas aeruginosa. 
Cystic fibrosis patients infected with Burkholderia cepacia have an increased rate of mortality compared to those patients with Pseudomonas aeruginosa infections. In some cystic fibrosis patients, Burkholderia cepacia can cause a rapid fatality, as described, for example in Am. J. Respir. Crit. Care Med., 160:5, 1572–7 (1999).
The high level of antibiotic resistance demonstrated by most strains of Burkholderia cepacia severely limits therapeutic options for its treatment (Clinics Chest Med., 19:473–86 (September 1998)). Furthermore, unlike Pseudomonas aeruginosa, Burkholderia cepacia can cause epidemic spread among cystic fibrosis patients and therefore any patient infected with Burkholderia cepacia is usually isolated from other patients. This causes both additional expenses connected with caring for these patients and may also be psychologically devastating to the patient. Furthermore, most lung transplant centers will not perform a lung transplant on patients infected with Burkholderia cepacia (Clinics Chest Med., 19:473–86 (September 1998)). Therefore, the Burkholderia cepacia infection is often viewed as a death sentence by patients with cystic fibrosis.
Burkholderia cepacia is usually resistant to the parenteral delivery of various antibiotics, including aztreonam, with showing only 5% of isolates to be sensitive to such treatment (Antimicrob. Agents Chemother., 34:3, 487–8 (March 1990)). Thus it would be advantageous to have available treatment for Burkholderia cepacia infections.
Other gram-negative bacteria intrinsically resistant to tobramycin can also complicate the care of a cystic fibrosis patient. These bacteria include Stenotrophomonas maltophilia and Alcaligenes xylosoxidans. Antibiotic therapy of these infections is usually also ineffective or leads to rapid emergence of drug resistance. Therefore, the successful treatment of all these infections requires that samples of these isolates are sent to a laboratory for complex antibiotic synergy determination of proper therapy for each individual patient (Ped. Pulmon., S17:118–119 (1998)). It would, therefore, be also advantageous to provide a therapy for these rare but hard to treat bacterial infections.
Similarly, the development of P. aeruginosa infection with strains which are resistant to, that is which have a high minimal inhibitory concentration (MIC) to a majority of antibiotics including tobramycin, predicts declining lung function and also may disqualify the patient from consideration for lung transplant (Clinics Chest Med., 19:535–554 (September 1998)).
Existing antibiotic treatments for Burkholderia cepacia, Stenotrophomonas maltophilia, Alcaligenes xylosoxidans, and multidrug resistant Pseudomonas aeruginosa pulmonary infections are either ineffective, or lead to rapid emergence of drug resistance.
From the brief description above, it is clear that there is a continuous need for an effective therapy for treatment of acute and chronic pulmonary bacterial infections caused by gram-negative bacteria and particularly those caused by Burkholderia cepacia, Stenotrophomonas maltophilia, Alcaligenes xylosoxidans, and multidrug resistant Pseudomonas aeruginosa lung infections. Such therapy would preferably comprise an inhalation of the aerosolized drug formulation delivering a therapeutically effective amount of the drug directly to the endobronchial space of airways to avoid systemic treatment.
The problems connected with infections caused with these antibiotic resistant bacteria are very serious and it would be advantageous to have available more efficient modes of treatments with different types of antibiotics.
Aztreonam is a synthetic antibiotic which has a good biological activity against gram-negative bacteria and it has previously been used for intravenous treatment of bacterial infections. However, its use is severely limited due to its low efficacy requiring administration of very large intravenous doses between 1000 and 4000 mg a day in order to treat the infections caused by gram-negative bacteria. Although it would be an antibiotic of choice for complementary treatment of patients treated with tobramycin or other antibiotics, particularly in cystic fibrosis patients, such treatment is not practical because of the high doses required.
Moreover, aztreonam is currently only available as an arginine salt. Arginine has been shown to be toxic to the lung and causes lung tissue irritation, inflammation, bronchospasm and cough and therefore is not suitable for a delivery by aerosolization. Consequently, aztreonam arginine salt is not approved for inhalation use in the United States or elsewhere.
However, as the antibiotic for treatment of pulmonary bacterial infections caused by gram negative bacteria, aztreonam could become a drug of choice for such treatment, if it could be delivered by inhalation in therapeutically effective concentrations directly to the lungs and if the problems connected with the aztreonam arginine can be overcome.
However, the efficacious administration of aztreonam by inhalation is further complicated by a lack of safe, physiologically acceptable and stable formulations for use by inhalation. Such formulation must meet several criteria, such as certain size range of inhalable particles, certain pH range and certain degree of salinity. When the aerosol contains a large number of particles with a mass medium average diameter (MMAD) larger than 5μ, these are deposited in the upper airways decreasing the amount of antibiotic delivered to the site of infection in the endobronchial space of airways. Similarly, both highly acidic and alkaline or hypotonic or hypertonic conditions lead to respiratory complications, such as bronchospasm and cough, preventing inhalation of the drug.
Thus it would be advantageous and desirable to provide an inhalable formulation for delivery of aztreonam by aerosol or a dry powder formulation for treatment of pulmonary gram-negative bacterial infections and particularly those caused by drug resistant strains Burkholderia cepacia, Stenotrophomonas maltophilia, Alcaligenes xylosoxidans, and multidrug resistant Pseudomonas aeruginosa, wherein the formulation comprises a smallest possible therapeutically effective amount of drug in a form which does not cause pulmonary inflammation, wherein the pH is adjusted to physiologically acceptable levels, wherein the aqueous solution is isotonic and wherein said formulation has adequate shelf life suitable for commercial distribution, storage and use.
It is, therefore, a primary object of this invention to provide a method for treatment of gram-negative infections, especially those caused by Burkholderia cepacia, Stenotrophomonas maltophilia, Alcaligenes xylosoxidans, and multidrug resistant Pseudomonas aeruginosa by providing a safe, physiologically acceptable and efficacious formulation for inhalation using a pure concentrated aztreonam free base, or a pharmaceutically acceptable salt thereof, which formulation contains sufficient but not excessive concentration of the active drug, which formulation can be efficiently aerosolized by nebulization using jet, ultrasonic or atomization nebulizers, into an aerosol having particle sizes within a range from 1 to 5μ, or administered as a dry powder, both well tolerated by cystic fibrosis patients and by patients with impaired pulmonary function due to infections, inflammation or another underlying disease.
All patents, patent applications and publications cited herein are hereby incorporated by reference.